All DL* categories are typically negative, but DLGSUP isn't, and it's also not
in libosmocore's internal_cat array.
See: 3b6fb0880c3ab1e23a3d7d738d073b00c2a794c2
This means that a program using DLGSUP has to include DLGSUP in its own logging
cat array (typically not needed for DL* categories), which means for osmo-nitb
that DLGSUP (11) replaces DMGCP (also 11), and DMGCP becomes unusable.
Fix this: make DLGSUP -11 and include in internal_cat.
In gsup_test.c, no longer add DLGSUP to the logging categories array.
External follow-ups are otherwise needed only in osmo-hlr.git and some pending
patches for openbsc (Id3938267fa062e1a997d3704cd678874306f86ee).
Change-Id: Id974c7be158e4d60421a98110f5c807aefd31119